Obesity, according to its cause, is classified into two groups, i.e. primary obesity (simple obesity) and secondary obesity (symptomatic obesity). The cause of primary obesity includes excessive energy intake, insufficient energy consumption and decreased thermogenesis. Today, primary obesity accounts for a large majority of diagnosed cases of obesity. Development and persistent of primary obesity may cause various health problems.
The secondary obesity is caused by certain underlying disorders and is also diagnosed as obesity. Examples of secondary obesity include endocrine obesity, hypothalamic obesity, hereditary obesity and drug-induced obesity.
Obesity is a risk factor for health. It may induce strain on the circulatory system, metabolic disorders such as diabetes, liver- or biliary-system disorders, respiratory depression as well as excessive weight on the bones and the joints.
Therapeutic approaches used for treating obesity include alimentotherapy, ergotherapy, behavioral therapy, psychotherapy and drug therapy. The alimentotherapy reduces the body weight by reducing total calorie intake with controlled diet. The method, however, often results in a lowered resting metabolic rate, which makes it harder to keep the weight off once the patient attained. Ergotherapy not only increases energy consumption, but also increases the resting metabolic rate and normalize the insulin resistance, and can effectively decrease the body fat. The big problem of the ergotherapy is the difficulty in carrying out the therapy continuously over a long period of time. The behavioral therapy and psychotherapy are carried out to support the alimentotherapy and/or ergotherapy, but they hardly bring sufficient effects.
Examples of the obesity drugs used for the drug therapy include appetite suppressant such as mazindol, fenfluramine, fluoxetine and cholecystokinin, agents to reduce digestive absorption such as acarbose, voglibose and lipostatin, agents to inhibit fat accumulation such as nafenopin, hydroxy oxalic acid and imidazole acetophen, and metabolic accelerators such as β3 receptor stimulant. However, such conventional obesity drugs may cause adverse side effects such as drug dependence, and patients having received such drugs may become resistant to the drugs in a short period. Accordingly, the conventionally used obesity drugs are not suitable for long term continuous treatment.
It has been desired in the art to develop an effective anti-obesity drug without or with decreased side effects, that can be continuously used for a long period without imposing burden on patients.
Prostaglandins (hereinafter, referred to as PG(s)) are members of class of organic carboxylic acids, which are contained in tissues or organs of human or other mammals, and exhibit a wide range of physiological activity. PGs found in nature (primary PGs) generally have a prostanoic acid skeleton as shown in the formula (A):

On the other hand, some of synthetic analogues of primary PGs have modified skeletons. The primary PGs are classified to PGAs, PGBs, PGCs, PGDs, PGEs, PGFs, PGGs, PGHs, PGIs and PGJs according to the structure of the five-membered ring moiety, and further classified into the following three types by the number and position of the unsaturated bond at the carbon chain moiety:    Subscript 1: 13,14-unsaturated-15-OH    Subscript 2: 5,6- and 13,14-diunsaturated-15-OH    Subscript 3: 5,6-, 13,14-, and 17,18-triunsaturated-15-OH.
Further, the PGFs are classified, according to the configuration of the hydroxyl group at the 9-position, into α type (the hydroxyl group is of an α-configuration) and β type (the hydroxyl group is of a β-configuration).
PGE1 and PGE2 and PGE3 are known to have vasodilation, hypotension, gastric secretion decreasing, intestinal tract movement enhancement, uterine contraction, diuretic, bronchodilation and anti ulcer activities. PGF1α, PGF2α and PGF3α have been known to have hypertension, vasoconstriction, intestinal tract movement enhancement, uterine contraction, lutein body atrophy and bronchoconstriction activities.
However, it is not known how prostaglandin compounds act on obesity.